Craving sugar? Why it’s not lack of willpower but your gut bacteria that’s to blame
DESPITE everything i’ve done to improve my diet, like most people, i still get those occasional mad, crazy cravings for junk food, the stuff that we all know is bad for us but which, despite our best intentions, we just can’t resist.
in my case, it’s chocolate, biscuits or cake. that’s why we rarely have them in our house, otherwise i could easily eat a whole packet or most of a cake in a single sitting.
However, i’ve discovered that if i ‘surf the urge’, these cravings normally pass. surfing the urge means that, rather than trying to fight it, i try to ride it out by
drinking a large glass of water, practising deep breathing and trying to focus on other things. it normally takes about 30 minutes before i am back in control.
But where do these crazy cravings come from? Junk food manufacturers are partly to blame because they are adept at creating food with just the right mix of fat, sugar, salt and flavourings that we find irresistible.
However, recent research from pittsburgh University in the U.s. has also shown, for the first time, how the microbes that live in the gut drive cravings for certain foods.
One way they do this is via the vagus nerve, the longest nerve in the body that connects the brain and the gut. it acts like a busy internet cable, sending lots of messages in both directions. there’s evidence, mainly from animal studies, that, similar to cyber attackers, your gut microbes can hack into this system and talk directly to your brain.
THESE microbes, which are brilliant chemists, can also turn the food that we eat into a range of hormones and chemical messengers that reach the brain via the bloodstream and, by doing so, influence our mood and our food preferences.
there are lots of examples of microbes manipulating other animals. Mice, when infected by bacteria called toxoplasma gondii, become strangely reckless. Normally, a mouse will keep to the shadows and avoid anything to do with cats. But when infected by toxoplasma they become attracted by the smell of cat urine and will boldly move out into the open, to be killed and eaten.
this happens because the toxoplasma bacteria need to infect a cat to complete their life cycle, and the only way to do this is to manipulate the mouse’s behaviour, turn it into a kamikaze mouse.
How the bacteria do this is a bit of a mystery, but one theory is that they interfere with the mouse’s reward centres in the brain, producing surges in dopamine and serotonin, ‘feelgood hormones’, which, unexpectedly, makes the smell of cat urine irresistible.
A similar mechanism seems to be at play in the recent study which looked at how gut microbes manipulate food preferences. the researchers infected laboratory mice with microbes from the guts of wild mice, chosen because they have very different natural diets.
some wild mice, given a choice, will opt for a high-protein, lowcarb diet, while others prefer a diet lower in protein and higher in carbs. When their gut microbes were transplanted into the laboratory mice, the mice changed what they ate in line with the preferences of the donor mice.
those given microbes from protein-loving rodents now went for a protein-rich diet, while the mice with microbes from the carb lovers soon became carb lovers.
And the researchers also noticed that introducing these new gut microbes also changed their levels of tryptophan, a substance that’s converted in our brains into serotonin. this strongly suggests that microbes, living in the mouse guts at least, were making and using tryptophan to manipulate what their host ate.
the message we can take from all this is that if you eat a junk food diet then this will probably encourage the growth of microbes in your gut that love junk food — and they will encourage you to eat more.
But if, instead, you increase the amount of fibre in your diet (eating more veg and wholegrains), this encourages the growth of other, more healthy bacteria, and these, in time, should help drown out the seductive chemical messages from the junk food-loving microbes telling you to ‘eat that biscuit, you know you want to’.
something else that can help fight cravings is exercise. Becoming more active will improve your mood, which should help reduce cravings, and encourages the growth of ‘good’ bacteria.
Another recent study showed that rats encouraged to run vigorously on a treadmill for a month ate far fewer unhealthy treats when offered than rats that led a more sedentary life. Although cravings for junk food are unlikely ever to die completely, changing your microbiome should make them easier to resist.